Sauropod tails: up or down?

By now even the media (well most of it) has cottoned onto the fact that sauropods did not drag their tails along the ground like giant lizards, but instead held them off the ground behind them. Except, well, not quite always.

While sauropod footprints are common, there are the occasional set of tracks that also show a mark that is interpreted as (and can only really be) that left by a tail dragging on the ground behind. So what’s going on, is the tail up or down?

Dinosaur tail drag mark. Image modified from Li et al., 2006.

The tracks look like this one. It’s actually an ornithischian tail drag, but it’s the only image I could find (borrowed from Li et al., 2006.), still the morphology is pretty similar to the sauropod drags I’ve seen so it’ll do for now. The can be short or long (this one is obviously very long) but quite narrow and have this sinusoidal curvature which is what you’d expect from a tail that shifted from side to side as the animal walked. So if sauropods are leaving drag marks, is the tail up or down?

First off, let’s consider the frequency of these marks.These things are really quite rare, while I’m sure there’s more out there, I’ve only seen reference to a handful in the literature when there are probably hundreds of sauropod trackways out there. That’s perhaps not surprising as the average sauropod is a pretty hefty animal and is going to be leaving tracks most places it goes, and if they heavy tail is really dragging on the floor then surely the drag marks will be pretty common.

Of course they remain rare because the tail is (largely) held off the ground. In most cases, the tail never dips down to leave a mark, even in places where the substrate is very soft and would pick up traces from something very light. So the rare occasions when we do get such traces were probably from unusual circumstances such as animals with especially long tails, or those walking on a slope or something like that. The traces we do have are also very narrow, so it’s clearly the very end of the tail that’s leaving the mark and not a more proximal, wider and heavier part. Thus despite the odd trackway showing up with a tail drag mark, this really provides confirmation that the tail was held of the ground and not dragged along as used to be depicted.

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9 Responses to “Sauropod tails: up or down?”

I wouldn’t be surprised to find tail drag marks in dinosaur tracks being underreported in the literature. I’ve always felt that the view of dinosaurs holding their tails skyward all the time seemed to be based more on aesthetics than biology (fallout from the dinosaur renaissance).

That’s not to say that I think that dinosaurs were dragging their tails everywhere; just that they weren’t held nearly as straight and erect as we always see them depicted.

I can understand keeping a stiff beam for the counterbalancing back end of theropods, but not for sauropods, or most ornithischians. Keeping the portions of the tail that housed the m. caudofemoralis, straight, makes sense (increasing the moment arm, and efficiency of the muscle). Beyond this point, I don’t see a reason to keep the tail aloft (seems like a waste of energy). I suspect that dinosaur tails probably drooped towards their distal ends; though likely did not touch the ground as the sheer height of the animals would prevent that from happening.

On a side note, most lizards only drag their tails when walking slowly. During trots (the usual mode of lizard transport) and runs, the tail is usually held well off the ground (straight up in some species; which is just weird). Mammals on the other hand, usually do drag their tails. It’s just that mammal tails are usually so dinky and small that they never reach the ground.

Well there is obviously a complex of things here and as ever I’m trying to cover the simplest aspects of it in review. I’m not sure it’s a waste of energy to keep the tail off the ground as it’s probably not that hard depending on how vertebral articulations are arranged plus ossified tendons, muscles etc. etc. etc. – it may not take any effort in some to hold them straight out, or at least be minimised. A colleagues is actually working on these kinds of problems at the moment so expect more in the future. The tails are somewhat homogeneous in most cases so once you keep the base straight, the rest will likely follow (though you do get a kink in some prosauropods for example, but even then they straighten up). Even in most sauropods I think the counterbalalnce argument still works to a degree (even with an upright neck) as it will likely be an energy save and help maintain balance, as it would in even the heavy quadrupedal ornithischians. WHile I agree that tail drags are probably underreported, they are still very rare, even when tracks are fine and immacualtely preserved which suggests they are genuinely absent and tails did not habitually drag.

Certainly some I would expect to droop like the distal end of diplodocoid tails where there bones are jsut tiny rods and there would likely have been little musculature or anything else there to hold it up, but I think in most cases a pretty straight-out tail is to be expected. I don’t know much about lizard anatomy, but I think their tails are built rather differently and certainly not all of the can hold the tail free of the ground (I’ve never seen skinks or iguanas do it, and racerunners are obviously at a huge disadvantage here).

Just a minor reply to Jura’s comment: the mammals that have short tails that do not reach the ground can afford for them to hang down. But when one of our cats lets her tail drag, she’s very sick and tired. There’s an expression “His tail is dragging” meaning “He’s out of energy.”

I can easily imagine that sometimes dinos got tired. Especially if they were running from danger. I wonder if the tail tracks are found associated with other dino tracks, with the other dino chasing his intended meal.

I suppose that dinosaurs may have had a system of body language. In dogs a certain degree of wagging the tail can indicate the relative emotion of that animal. While very different animals, we find that cats and dogs give strong indications of tail expression, they are both carnivora I believe.

While mammals usually have short tail, suppose the long whip-like tail of a diplodicid would have enough dexterity to have a significant amount of shape to work with.

We could only postulate about commonalities of the neurology and psychologies of dinosaurs but most dinosaurs do share a prominent physiological existence with their tails whether it be decorative feathers, clubs or thagomizers.

I suppose that such tail choreography from a long tailed sauropod could create a motion that may imitate cursive writing as a long twirling whip could do. While a whip is dumb, a motor nerve innervated whiptail could possibly convey such sauropod emotions. While smaller dinosaurs containing pygostyles are assumed to have fanning tail feathers possibly indicating a function for sexual attraction via whip-tail flaunting.

Its probable that sauropod tails are habitually held up. I dont know, I just had this on my mind and had to type it out before I forget.

If the phrase in Job 40:17 (“…he moveth his tail as a cedar…”) is rendered directly from the Hebrew, we get “…he inclines his tail as a firm cedar….” This was God (the Creator of these marvelous creatures) speaking and demonstrating that He knew in anatomical detail this animal He claims to have made on day 6 with man.

So why is behemoth not mentioned in Genesis 1:24? In English, it is not – BUT the English word cattle is actually the Hebrew word Behemoth! In fact, Behemoth is used another 55 times in the Old Testament and exclusively in the first 10 chapters of Genesis when the reference is to a specific animal and not miqneh = acquired livestock.

God told Job that He created these critters, left a clear description that rules out an elephant (wrong tail size and not held erect behind) or a hippo (tail is really just a flap of tissue). The ONLY critter that fits this description is what we today would call Brachiosaurus – and I repeat, this word is used nearly 60 times in the Old Testament.

Details in the book Behold Now Behemoth: Dinosaurs All Over the Bible!

I’ve let this comment through, but obviously I disagree profoundly. The entirity of this argument is a ‘tail like a cedar’ is a) literal, b) contains no errors, and c) apparently shows ‘anatomical detail’. anyone who thinks this could only correspond to a Brachiosaurus (of dinosaurs generally, let alone all animals) is severly lacking in knowledge of biology.

It doesn’t say ‘trunk’ though, does it? It says “as a cedar”, which could be a branch, or a twig, or a set of leaves, or the trunk of a young tree etc. etc. etc. And I didn’t say it had anything to do with living animals either, did I? You’re adding specifics where they don’t exist and then attempting to use this to prove the point.

Now please, don’t you or others come over here and try and argue this point to death. We all know neither or us are going to agree, so don’t please waste my time or yours ‘debating’ this point.